Is it possible already?

Yoshi was dx'd a week ago last Wednesday. One weekend of 1 unit 2x day, then a couple days at the vet to check his sugar all day, where his glucose was only a tad high. Reduced the dose to 1/2 unit 2x a day. He had his last shot Saturday evening, then Sunday morning I managed to check his blood sugar before giving him the shot - 57! (Also a win for me, I finally figured out a method that works for us to get his blood sugar checked!) Needless to say he got his noms a bit faster and no shot. Later that evening before dinner, checked him again, 79! Wow, wish my blood sugar looked this good. No shot again. Today his bg has been 84 before breakfast, 72 a couple hours after breakfast, then 70 before dinner.
Is it possible he's in remission this fast?? Or is it more likely that he wasn't really full blown diabetic but just on a high carb diet and stressed at the vet??

It is definitely possible for a kitty to quickly go into remission, especially when their diet is changed from high carb to low carb. I know I've heard of some kitties who actually had something else going on and were misdiagnosed as diabetics, but I'm not sure how frequently that happens. With his BG at 381 at diagnosis, I would say we could call him a diabetic. The official protocol for an OTJ (Off the Juice) trial is for the kitty to be within normal BG range without any insulin for 14 days. So make sure you continue to get those am/pm preshot tests in during this time so you can ensure he is still not needing the insulin. Normal with a human glucometer is 50-120. If Yoshi goes the full 14 days without insulin, you can celebrate your diet-controlled kitty who will be considered in remission!! Lou and I will be rooting for you and Yoshi!!!

Some cats really do go into remission that quickly. Pants was on insulin for 10 days and after two hypos, we stopped the shots and diet alone has been enough to keep her pretty close to the normal range.

Did Yoshi have symptoms of diabetes? And did you get high numbers at home? That would help confirm that you've got the right diagnosis. Given the 381, though, it seems pretty likely he really is diabetic. My vet said that while there can be a pretty dramatic spike in a non-diabetic cat, once you're over 300, the cat's almost certainly diabetic. Most cats can't get there starting from a normal range, even under extreme stress.

Yoshi's very lucky that you know what you're doing and caught how quickly his numbers are falling!